1. Field of the Invention
The present invention relates to a noise damper for a pneumatic tire, more particularly to a band-shaped damper with a flap rising by a centrifugal force during running.
In recent years, as the mechanical noise from automobiles especially passenger cars has been greatly reduced, the tires especially passenger car tires are strongly required to reduce their noise. There are many factors in tire noise, but a circumferential resonance of the air in the annular tire cavity is a major factor. That is, a ring of air inside the tire which is continuous around the rim is excited by vibrations during running and resonates in the circumferential direction. Usually, a resonance peak occurs in a frequency range of from 50 to 400 Hz according to the tire size.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97-1.99
In published Japanese patent JP-B-7-14682 (application No. 61-284973), an assembly of a wheel rim and a pneumatic tire mounted thereon is disclosed, wherein a ball-like body which is made of rubber, sponge or the like is put in the annular tire cavity to block the circumferential continuity thereof to control resonance. Such a ball-like body is however, liable to disturb the high-speed rotational balance of the tire because the inner surface of the tire receives a full gravity of the ball-like body which increases as the rotational speed increases. Further, it has a tendency to make it difficult to mount the tire on a wheel rim.
In published Japanese patent application JP-A-8-132816 (application No. 6-303174), an assembly of a wheel rim and a pneumatic tire mounted thereon is disclosed, wherein unwoven fabric is applied to the inner surface of the tire as a sound absorber. It is however, difficult to fully control resonance.
In published Japanese Utility Model application JP-U-63-112905 (application No. 62-4990), an assembly of a wheel rim and a pneumatic tire mounted thereon is disclosed, wherein a band-like continuous urethane rubber is disposed around the wheel rim loosely and fixed to the rim well at four points at regular intervals in the circumferential direction so that the portions of the urethane rubber between the fixed points bulge out like an arch due to centrifugal force during running. In this case, it is difficult to obtain a sufficient rising height at a relatively low running speed, and more work is necessary to fix the urethane rubber.
It is therefore, an object of the present invention to provide a noise damper to be disposed in an annular tire cavity formed between a wheel rim and a pneumatic tire mounted thereon, which is easy to fix and which can effectively reduce a tire noise due to circumferential resonance of the air in the tire cavity without disturbing the high-speed rotational balance of the wheel.
According to the present invention, a noise damper comprises an annular band-like body made of an elastomeric material, the annular band-like body provided with at least one generally U-shaped cut oriented in a circumferential direction, whereby a cutout by the at least one generally U-shaped cut forms a flap which is risen by a centrifugal force during running, and the remainder forms a base band to be put around a bottom of the wheel rim in an elongated condition to secure the flap.
The flap may have a relatively long length such that, when risen, a radially outer end portion thereof comes into contact with the radially inside of a tread portion of the tire so that a main portion which traverses the tire cavity is subjected to variable bending deformation during running. Therefore, resonance conditions are varied, and the noise due to resonance of the air in the tire cavity can be effectively reduced in not only the fundamental mode but also the higher harmonic modes along the circumferential length of the tire cavity.
The at least one generally U-shaped cut for forming a flap may be two opposite U-shaped cuts wherein an open end of the U-shape of one of the U-shaped cuts enters in the U-shape of the other U-shaped cut from an open end thereof without intersecting each other. In this case, the length of the flap is increased although the apparent circumferential length is short. Thereby, it becomes possible to increase the number of the long flaps.
Further, the flap may be made of nonwoven fabric at least partially, for example it is possible to make one side of the flap with unwoven fabric. In this case, the resonance of the air in the tire cavity can be effectively damped in not only the fundamental mode but also the higher harmonic modes.
For the rotational balance of the wheel, it is important that the rising flaps are arranged evenly around the rotational axis. However, even arrangement tends to induce resonance in higher harmonic modes causing high frequency noise because there is a possibility that a standing wave having nodes positioned at the rising flaps occurs although the resonance in the fundamental harmonic mode can be effectively controlled. If the surface of the flaps is hard and flat, such is remarkable. By using the longer flap or unwoven fabric, the resonance in higher harmonic modes can be effectively reduced.